Japanese Patent Publication NO. 2560025 discloses a conventional electric toothbrush. This electric toothbrush has a handle to be grasped by user, a vibration unit accommodated within the handle for vibrating a shaft along its axis. The shaft is detachably connected to a brush head, and driven to vibrate the brush head by the vibration unit. This electric toothbrush is designed to flow a micro-electric current through user's body into portion of a user's oral cavity in contact with the brush head, for removal of tooth plaque. This electric toothbrush is equipped with a source of micro-electric current having one pole connected to a touch electrode for contact with user's hand at an outer perimeter of the handle, and the other pole connected to the electrically conductive shaft by way of a connecting metal part, so as to give a predetermined electric potential to the brush head. This connecting metal part is formed as a contact spring having its one end to slide on the shaft for an electrical connection.
However, the connecting metal part is designed to have a contact portion at its one end for sliding on the shaft, causing unevenness in the electric current flowing within the user's oral cavity by a variance in the electric resistance of the connecting portion between the shaft and the connecting metal part in response to bending of the shaft by user's force toward his/her teeth and deflection of the shaft due to vibration of the shaft during user's tooth brushing.